DE 199 49 604 A1 describes a method according to which a hearing aid is delivered to a dealer in a basic version, wherein it is possible to functionally upgrade the hearing aid using a chip card. An integrated circuit of the hearing aid is, accordingly, provided initially programmed so as to provide only basic functionalities, and then, said integrated circuit is programmed, so as to provide additional functionalities.
US 2002/0054689 A1 describes a method for upgrading a hearing device. The upgrading process requires an online connection to a remote server.
WO 2006/002035 A2 describes a low-cost, time limited hearing health aid, which is intended for temporary, evaluative purposes. The hearing health aid comprises a counter, and after a predetermined count is reached by the counter, operations of the hearing health aid will be disabled.